It is often necessary to evaporate solvents from a solution or suspension as a step in processing or concentrating a sample of material for instrumental analysis. For example, in the geological and environmental sciences, one needs to evaporate solvent from samples of solvent extracts of sediment and soil samples, as well as various fractions of compounds resulting from chromatographic isolation steps.
Gas often needs to be introduced to multiple reaction vessels during parallel reactions or synthesis such as hydrogenation of unsaturated organic compounds. The standard method for accomplishing these is to pass a gas that is under pressure over the surface of the sample or into the solution. The configuration of the sample holder, the temperature of the sample and/or of the pressurized gas, the composition of the gas and the need to work in an environment where human exposure to the sample and gas is controlled are features which are well recognized as affecting the desired evaporation.
Individual samples are easily processed. For example, a sample of soil extracts suspended in ethanol and contained in a test tube might be dried by evaporation of the ethanol solvent by passing a stream of pressurized nitrogen gas through a pipette over the sample.
However, often one needs to process a number of samples for analysis. Devices which can be used to facilitate multiple samples processing including those that hold multiple samples and those which use evaporators capable of delivering several streams of pressurized gas simultaneously are known. For example, see the 6-Port Mini-Vap, item 201006 in the online catalog at www.chromes.com or the MiniVap Sample Concentrator in the online catalog of Artic White (www.articwhiteusa.com).
Shortcomings of known devices, such as those above, include the fact that the flow of gas from all nozzles in an evaporator is not equal and individual nozzles can not be controlled individually (that is, all are on or all are off). This leads to disparity in the rate of evaporation of solvent such that at any given time, some samples are dried faster than others and this can lead to undesired variations in subsequent processing steps or analyses. Also, the “all-on or all-off” configuration can lead to waste of the pressurized gas if not all nozzles in a evaporator are being used, and also cause dust/contaminants being blown up from unused ports that can contaminate samples in ports being used. When concentrating solutes with relatively high volatility, excessive blowing with nitrogen when solvent is already removed can lead to sample losses and subsequent error in analytical results.
In view of the foregoing, there is a need for a high-throughput evaporator to provide an even gas distribution for multiple samples. In addition, there is a need for an evaporator that has adjustable and independent flow control over gas exiting the evaporator for each sample. Also, there is a need for an evaporator that minimizes the leakage of gas.